Cortisol is essential to milk synthesis; however, different acute stressors and the exogenous administration of adrenocorticotropic hormone (ACTH) decrease milk yield. Therefore, the effect of cortisol on milk yield and its influence on the survival of mammary epithelial cells have not been fully elucidated. In this context, the objective of this study was to evaluate the effect of cortisol on the expression of growth hormone receptor (GHR), insulin-like growth factor type 1 (IGF1), insulin-like growth factor type 1 receptor (IGF1R), insulin-like growth factor-binding protein 3 and 5 (IGFBP3 and IGFBP5), BAX, and BCL2 genes on the proliferation and apoptotic rates of mammary epithelial cells, and on milk yield in Saanen goats. In the present study, 3 experiments were conducted: (1) comparing the in vivo effects of first milking, vaccination, vermifugation, preventive hoof trimming, and the administration of ACTH or a placebo on cortisol release in dairy goats; (2) studying the in vivo effects of immediate increases in cortisol on the mammary gland of lactating goats; and (3) studying the in vitro effects of a prolonged increase in cortisol on mammary epithelial cells obtained from lactating goats. Cortisol release by goats increased significantly after ACTH administration compared with that observed after a placebo, and the cortisol profiles after first milking, vaccination, vermifugation, hoof trimming, and ACTH administration were similar. However, there was no effect of the immediate increase in cortisol in vivo on IGF-1 release, milk yield, milk quality, or the apoptosis and proliferation rates, nor was there any effect on the expression of the target genes. Furthermore, no interaction was observed between IGF-1 and cortisol in either the in vivo or in vitro experiments. However, the addition of cortisol in vitro significantly increased the expression of the GHR and IGF1R genes, which stimulate cell proliferation, and the BAX gene, which causes apoptosis. These contrasting results can explain why cortisol did not change the rates of proliferation or apoptosis in epithelial cells. Indeed, cortisol supplementation in vitro did not change the number or apoptotic rate of epithelial cells over the course of 5 d. Finally, further studies must be performed to understand the effect of cortisol on the expression of the GHR, IGF1R, and BAX genes by epithelial cells and the roles of these genes in milk synthesis during early lactation.

Little is known about the effects of heat stress during the late gestation period on lactation in dairy goats. For this reason, 32 Saanen goats were randomly assigned to 1 of 2 groups, control (CT; n = 16) or heat stress (HS; n = 16), during late gestation. The HS goats were housed in a climatic chamber before parturition and subjected to heat stress for the last 45 d. After parturition, the HS goats were housed in the same conditions as the CT group. Mammary gland biopsies were performed on 7 goats per treatment at −30, −15, 15, and 30 d relative to parturition, so that the expression levels of several genes could be determined. The HS goats produced less milk than the CT goats did during the first half of lactation, but not during the rest of lactation. Before parturition, apoptosis-related transcripts (TP53 and BAX) were higher in the mammary glands of the HS goats than in those of the CT goats. The HS goats also had higher levels of HSPB1 gene expression during gestation and lactation. However, expression of the prolactin receptor gene was lower after parturition in the mammary glands of HS, suggesting downregulation of prolactin signaling. In summary, heat stress during final gestation reduces milk yield in the subsequent lactation. Although the upregulation of apoptosis signaling in the HS goats suggests that heat stress affects mammary cell number, the loss of the effect on milk production is more compatible with an effect on cell activity, which could be due to a downregulation of prolactin signaling.

No abstract

Estudou-se no estuário de Cananéia, litoral do estado de São Paulo, Brasil, a presença de Ascocotyle (Phagicola) longa Ransom, 1920 (Digenea: Heterophylidae), trematódeo, em tainha (Mugil platanus, Günther, 1880). Foram realizadas amostragens a fresco e cortes histológicos em tecidos provenientes de 61 exemplares. A presença de metacercárias foi comprovada em 100% dos peixes examinados, com a seguinte distribuição: coração (21,6%), fígado (19,7%) e rins (58,6%). As alterações histológicas no tecido cardíaco foram caracterizadas pela presença de um granuloma parasitário formado por uma cápsula de tecido conjuntivo ao redor do parasita, levando a um edema generalizado. Para determinar a infecção em alevinos de tainha da espécie M. platanus, foram capturados 100 exemplares nas entradas de córregos da região estuarino-lagunar. Esses peixes foram eviscerados para a pesquisa de metacercárias pelo exame a fresco, verificando-se que 100% dos alevinos não estavam infectados.